埃塞俄比亚欧加登次盆Karoo期碎屑岩成藏组合地质特征与勘探潜力

Geological characteristics and exploration potential of Karoo clastic play, Ogaden Basin, Ethiopia

王建君 李浩武 王青 胡湘瑜 周超 赵旭

Wang Jianjun Li Haowu Wang Qing Hu Xiangyu Zhou Chao Zhao Xu

中国石油勘探开发研究院, 北京 100083

Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China

Karoo期碎屑岩成藏组合是欧加登次盆最重要的天然气成藏组合,Bokh组泥质烃源岩与Calub和Adigrat组砂岩构成了成藏组合最基本的源储要素。在系统解剖油气成藏要素的基础上,认为Karoo期碎屑岩成藏组合发育断块、低幅度背斜、岩性尖灭、下切河道和透镜砂体等圈闭类型。区域性古隆起决定了油气富集区的平面展布,圈闭形成时间决定了充注的有效性,要尽量寻找Bokh组烃源岩白垩纪晚期大规模生排气之前就已形成的圈闭。盆地北部Adigrat组以中—粗砂岩为主,Bodle深埋区以细砂岩为主,宏观上Adigrat组下段物性优于上段,下段将主要以构造型圈闭为主,上段可发育岩性体圈闭。由于Calub组上源下储的格局,侧向运移将占主导地位,盆地内古"凹中隆"最为有利,同时斜坡部位的岩性尖灭体也具有较大潜力。Calub古隆起及周边Calub和Adigrat组储层发育条件最好,断裂体系发育,构造曲率变化大,又处于生烃中心围限中,油气成藏配置条件最佳,是最现实的主攻目标区。

The Karoo clastic play is the most important gas play in the Ogaden Basin. The Bokh mudstones and the Calub and Adigrat sandstones worked as source rocks and reservoirs. Various traps developed in the Karoo clastic play, including faulted blocks, low-amplitude anticlines, lithologic pinchouts, channel sands and lens-shaped sand bodies. The distribution of regional paleo highs controlled the planar accumulation of hydrocarbon while trap formation timing determined the effectiveness of hydrocarbon charging. The traps which formed before the Late Cretaceous should be most efficient, for the Bokh source rocks had entered the gas window at that time. But in the following history, uplift took place in most parts of the Ogaden Basin, and the maturity of source rocks changed little. The Adigrat Formation has coarse sandstones in the northern basin and fine sandstones in the Bodle deep. The lower Adigrat Formation has better physical properties than the upper section. Structural traps are dominant in the lower part, while lithologic traps develop in the upper part. For the Bokh source rocks lay above the Calub reservoir, lateral migration was important for hydrocarbon accumulation. Intra-sag paleo highs are the most favorable, and the pinch outs in the basin slope also have a good potential. The Calub paleo high is a realistic exploration target since it is surrounded by the Bokh source rocks, where the Calub and Adigrat reservoirs were well developed. A widespread fracture system and various structural orientations also contribute to hydrocarbon migration and accumulation.

国家科技重大专项"全球剩余油气资源研究及油气资产快速评价技术"(2011ZX05028)资助。

https://doi.org/10.11781/sysydz201504479